September 11 attacks, also called 9/11 attacks, series of airlinehijackings and suicide attacks committed by 19 militants associated with the Islamic extremist group al-Qaeda against targets in the United States, the deadliest terrorist attacks on American soil in U.S. history. The attacks against New York City and Washington, D.C., caused extensive death and destruction and triggered an enormous U.S. effort to combat terrorism. Some 2,750 people were killed in New York, 184 at the Pentagon, and 40 in Pennsylvania (where one of the hijacked planes crashed after the passengers attempted to retake the plane); all 19 terrorists died (seeResearcher’s Note: September 11 attacks). Police and fire departments in New York were especially hard-hit: hundreds had rushed to the scene of the attacks, and more than 400 police officers and firefighters were killed.

The routes of the four U.S. planes hijacked during the terrorist attacks of September 11, 2001.

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September 11, 2001, attack on the World Trade Center in New York City remembered.

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Hijacked airliner approaching the south tower of the World Trade Center.

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Fire and smoke billowing from the Pentagon after hijackers crashed American Airlines flight 77 into …

Cpl. Jason Ingersoll, USMC/U.S. Department of Defense

Part of the wreckage of United Airlines flight 93. The airplane was crashed into a field near …

United States District Court for the Eastern District of Virginia (U.S. v. Moussaoui)

Time-lapse video (2004–14) of the construction of the National September 11 Memorial & …

The September 11 attacks were precipitated in large part because Osama bin Laden, the leader of the militant Islamic organization al-Qaeda, held naive beliefs about the United States in the run-up to the attacks. Abu Walid al-Masri, an Egyptian who was a bin Laden associate in Afghanistan in the 1980s and ’90s, explained that, in the years prior to the attacks, bin Laden became increasingly convinced that America was weak. “He believed that the United States was much weaker than some of those around him thought,” Masri remembered, and “as evidence he referred to what happened to the United States in Beirut when the bombing of the Marines base led them to flee from Lebanon,” referring to the destruction of the marine barracks there in 1983 (see1983 Beirut barracks bombings), which killed 241 American servicemen. Bin Laden believed that the United States was a “paper tiger,” a belief shaped not just by America’s departure from Lebanon following the marine barracks bombing but also by the withdrawal of American forces from Somalia in 1993, following the deaths of 18 U.S. servicemen in Mogadishu, and the American pullout from Vietnam in the 1970s.

The key operational planner of the September 11 attacks was Khalid Sheikh Mohammed (often referred to simply as “KSM” in the later 9/11 Commission Report and in the media), who had spent his youth in Kuwait. Khalid Sheikh Mohammed became active in the Muslim Brotherhood, which he joined at age 16, and then he went to the United States to attend college, receiving a degree from North Carolina Agricultural and Technical State University in 1986. Afterward he traveled to Pakistan and then Afghanistan to wage jihad against the Soviet Union, which had launched an invasion against Afghanistan in 1979.

Khalid Sheikh Mohammed.

United States District Court for the Eastern District of Virginia (U.S. v. Moussaoui)

According to Yosri Fouda, a journalist at the Arabic-language cable television channel Al Jazeera who interviewed him in 2002, Khalid Sheikh Mohammed planned to blow up some dozen American planes in Asia during the mid-1990s, a plot (known as “Bojinka”) that failed, “but the dream of Khalid Sheikh Mohammed never faded. And I think by putting his hand in the hands of bin Laden, he realized that now he stood a chance of bringing about his long awaited dream.”

In 1996 Khalid Sheikh Mohammed met bin Laden in Tora Bora, Afghanistan. The 9-11 Commission (formally the National Commission on Terrorist Attacks Upon the United States), set up in 2002 by Pres. George W. Bush and the U.S. Congress to investigate the attacks of 2001, explained that it was then that Khalid Sheikh Mohammed “presented a proposal for an operation that would involve training pilots who would crash planes into buildings in the United States.” Khalid Sheikh Mohammed dreamed up the tactical innovation of using hijacked planes to attack the United States, al-Qaeda provided the personnel, money, and logistical support to execute the operation, and bin Laden wove the attacks on New York and Washington into a larger strategic framework of attacking the “far enemy”—the United States—in order to bring about regime change across the Middle East.

The September 11 plot demonstrated that al-Qaeda was an organization of global reach. The plot played out across the globe with planning meetings in Malaysia, operatives taking flight lessons in the United States, coordination by plot leaders based in Hamburg, Germany, money transfers from Dubai, and recruitment of suicide operatives from countries around the Middle East—all activities that were ultimately overseen by al-Qaeda’s leaders in Afghanistan.

Key parts of the September 11 plot took shape in Hamburg. Four of the key pilots and planners in the “Hamburg cell” who would take operational control of the September 11 attacks, including the lead hijacker Mohammed Atta, had a chance meeting on a train in Germany in 1999 with an Islamist militant who struck up a conversation with them about fighting jihad in the Russian republic of Chechnya. The militant put the Hamburg cell in touch with an al-Qaeda operative living in Germany who explained that it was difficult to get to Chechnya at that time because many travelers were being detained in Georgia. He recommended they go to Afghanistan instead.

Florida driver’s license photo of Mohammed Atta.

United States District Court for the Eastern District of Virginia (U.S. v. Moussaoui)

Discussion of Mohammed Atta, lead hijacker in the September 11, 2001, terrorist attacks, and German …

Although Afghanistan was critical to the rise of al-Qaeda, it was the experience that some of the plotters acquired in the West that made them simultaneously more zealous and better equipped to carry out the attacks. Three of the four plotters who would pilot the hijacked planes on September 11 and one of the key planners, Ramzi Binalshibh, became more radical while living in Hamburg. Some combination of perceived or real discrimination, alienation, and homesickness seems to have turned them all in a more militant direction. Increasingly cutting themselves off from the outside world, they gradually radicalized each other, and eventually the friends decided to wage battle in bin Laden’s global jihad, setting off for Afghanistan in 1999 in search of al-Qaeda.

Atta and the other members of the Hamburg group arrived in Afghanistan in 1999 right at the moment that the September 11 plot was beginning to take shape. Bin Laden and his military commander Muhammad Atef realized that Atta and his fellow Western-educated jihadists were far better suited to lead the attacks on Washington and New York than the men they had already recruited, leading bin Laden to appoint Atta to head the operation.

The hijackers, most of whom were from Saudi Arabia, established themselves in the United States, many well in advance of the attacks. They traveled in small groups, and some of them received commercial flight training.

Throughout his stay in the United States, Atta kept Binalshibh updated on the plot’s progress via e-mail. To cloak his activities, Atta wrote the messages as if he were writing to his girlfriend “Jenny,” using innocuous code to inform Binalshibh that they were almost complete in their training and readiness for the attacks. Atta wrote in one message, “The first semester commences in three weeks…Nineteen certificates for private education and four exams.” The referenced 19 “certificates” were code that identified the 19 al-Qaeda hijackers, while the four “exams” identified the targets of the attacks.

In the early morning of August 29, 2001, Atta called Binalshibh and said he had a riddle that he was trying to solve: “Two sticks, a dash and a cake with a stick down—what is it?” After considering the question, Binalshibh realized that Atta was telling him that the attacks would occur in two weeks—the two sticks being the number 11 and the cake with a stick down a 9. Putting it together, it meant that the attacks would occur on 11-9, or 11 September (in most countries the day precedes the month in numeric dates, but in the United States the month precedes the day; hence, it was 9-11 in the United States). On September 5 Binalshibh left Germany for Pakistan. Once there he sent a messenger to Afghanistan to inform bin Laden about both the day of the attack and its scope.

The attacks

On September 11, 2001, groups of attackers boarded four domestic aircraft at three East Coast airports, and soon after takeoff they disabled the crews, some of whom may have been stabbed with box cutters the hijackers were secreting. The hijackers then took control of the aircraft, all large and bound for the West Coast with full loads of fuel. At 8:46 am the first plane, American Airlines flight 11, which had originated from Boston, was piloted into the north tower of the World Trade Center in New York City. Most observers construed this initially to be an accident involving a small commuter plane. The second plane, United Airlines flight 175, also from Boston, struck the south tower 17 minutes later. At this point there was no doubt that the United States was under attack. Each structure was badly damaged by the impact and erupted into flames. Office workers who were trapped above the points of impact in some cases leapt to their deaths rather than face the infernos now raging inside the towers. The third plane, American Airlines flight 77, taking off from Dulles Airport near Washington, D.C., struck the southwest side of the Pentagon (just outside the city) at 9:37 am, touching off a fire in that section of the structure. Minutes later the Federal Aviation Authority ordered a nationwide ground stop, and within the next hour (at 10:03 am) the fourth aircraft, United Airlines flight 93 from Newark, New Jersey, crashed near Shanksville in the Pennsylvania countryside after its passengers—informed of events via cellular phone—attempted to overpower their assailants.

Photograph from a security camera at the Portland, Maine, airport showing lead hijacker Mohammed …

United States District Court for the Eastern District of Virginia (U.S. v. Moussaoui)

A hijacked commercial plane approaching the World Trade Center shortly before crashing into the …

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Smoke and flames erupting from the twin towers of New York City’s World Trade Center after the …

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Aerial photograph of the destruction following the crash of a hijacked plane into the Pentagon on …

Tech. Sgt. Cedric H. Rudisill/U.S. Department of Defense

Wreckage of United Airlines flight 93, which was crashed during the terrorist attacks of September …

United States District Court for the Eastern District of Virginia (U.S. v. Moussaoui)

At 9:59 am the World Trade Center’s heavily damaged south tower collapsed, and the north tower fell 29 minutes later. Clouds of smoke and debris quickly filled the streets of Lower Manhattan. Office workers and residents ran in panic as they tried to outpace the billowing debris clouds. A number of other buildings adjacent to the twin towers suffered serious damage, and several subsequently fell. Fires at the World Trade Center site smoldered for more than three months.

Smoke and flames erupting from the twin towers of New York City’s World Trade Center after the …

Chao Soi Cheong/AP

Smoke billowing from the burning World Trade Center site following the September 11, 2001, …

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People fleeing as the south tower of the World Trade Center collapses as a result of the September …

Stock footage courtesy The WPA Film Library

Rescue operations began almost immediately as the country and the world sought to come to grips with the enormity of the losses. Nearly 3,000 people had perished: some 2,750 people in New York, 184 at the Pentagon, and 40 in Pennsylvania; all 19 terrorists also died. Included in the total in New York City were more than 400 police officers and firefighters, who had lost their lives after rushing to the scene and into the towers.

Man, covered in ash, assisting a woman holding a particle mask to her face as they walk in the wake …

Don Halasy/Library of Congress, Washington, D.C. (ppmsca.01811)

Firefighter calling for 10 additional rescue workers to make their way into the rubble of the World …

J01 Preston Keres/U.S. Navy

On the morning of September 11, President Bush had been visiting a second-grade classroom in Sarasota, Florida, when he was informed that a plane had flown into the World Trade Center. A little later Andrew Card, his chief of staff, whispered in the president’s right ear: “A second plane hit the second tower. America is under attack.” To keep the president out of harm’s way, Bush subsequently hopscotched across the country on Air Force One, landing in Washington, D.C., the evening of the attacks. At 8:30 pm Bush addressed the nation from the Oval Office in a speech that laid out a key doctrine of his administration’s future foreign policy: “We will make no distinction between the terrorists who committed these acts and those who harbor them.”

U.S. Pres. George W. Bush conferring with his chief of staff aboard Air Force One, September 11, …

Eric Draper/The White House

Pres. George W. Bush conferring with Vice Pres. Dick Cheney from Air Force One en route from …

Eric Draper/The White House

U.S. Pres. George W. Bush addressing the country from the Oval Office on September 11, 2001.

Eric Draper/The White House

U.S. Vice Pres. Dick Cheney talking on the phone with Pres. George W. Bush as National Security …

Eric Draper/The White House

On September 14 Bush visited “Ground Zero,” the smoking pile of debris of what remained of the World Trade Center and the thousands who had perished there. Standing on top of a wrecked fire truck, Bush grabbed a bullhorn to address the rescue workers working feverishly to find any survivors. When one of the workers said that he could not hear what the president was saying, Bush made one of the most memorable remarks of his presidency:

I can hear you. The rest of the world hears you. And the people who knocked these buildings down will hear from all of us soon.

Pres. George W. Bush addressing a crowd as he stands on rubble at the World Trade Center site in …

Eric Draper/The White House

U.S. Secretary of State Colin Powell describing the need for responding with equanimity to the …

Stock footage courtesy The WPA Film Library

Bush’s robust response to the attacks drove his poll ratings from 55 percent favourable before September 11 to 90 percent in the days after, the highest ever recorded for a president.

The aftermath

The emotional distress caused by the attacks—particularly the collapse of the twin towers, New York City’s most visible landmark—was overwhelming. Unlike the relatively isolated site of the Pearl Harbor attack of 1941, to which the September 11 events were soon compared, the World Trade Center lay at the heart of one of the world’s largest cities. Hundreds of thousands of people witnessed the attacks firsthand (many onlookers photographed events or recorded them with video cameras), and millions watched the tragedy unfold live on television. In the days that followed September 11, the footage of the attacks was replayed in the media countless times, as were the scenes of throngs of people, stricken with grief, gathering at “Ground Zero”—as the site where the towers once stood came to be commonly known—some with photos of missing loved ones, seeking some hint of their fate.

Notices and pictures of missing persons posted on a mailbox in New York City following the …

David Finn/Library of Congress, Washington, D.C. (ppmsca.01936)

Memorial to the victims of the September 11 attacks, New York City, 2001.

Moreover, world markets were badly shaken. The towers were at the heart of New York’s financial district, and damage to Lower Manhattan’s infrastructure, combined with fears of stock market panic, kept New York markets closed for four trading days. Markets afterward suffered record losses. The attacks also stranded tens of thousands of people throughout the United States, as U.S. airspace remained closed for commercial aviation until September 13, and normal service, with more rigid security measures, did not resume for several days.

The September 11 attacks were an enormous tactical success for al-Qaeda. The strikes were well coordinated and hit multiple targets in the heart of the enemy, and the attacks were magnified by being broadcast around the world to an audience of untold millions. The September 11 “propaganda of the deed” took place in the media capital of the world, which ensured the widest possible coverage of the event. Not since television viewers had watched the abduction and murder of Israeli athletes during the Munich Olympics in 1972 had a massive global audience witnessed a terrorist attack unfold in real time. If al-Qaeda had been a largely unknown organization before September 11, in the days after it became a household name.

A discussion of how the AT&T Corporation coped with the massive increase in telecommunication …

After the attacks of September 11, countries allied with the United States rallied to its support, perhaps best symbolized by the French newspaper Le Monde’s headline, “We are all Americans now.” Even in Iran thousands gathered in the capital, Tehrān, for a candlelight vigil.

Evidence gathered by the United States soon convinced most governments that the Islamic militant group al-Qaeda was responsible for the attacks. The group had been implicated in previous terrorist strikes against Americans, and bin Laden had made numerous anti-American statements. Al-Qaeda was headquartered in Afghanistan and had forged a close relationship with that country’s ruling Taliban militia, which subsequently refused U.S. demands to extradite bin Laden and to terminate al-Qaeda activity there.

For the first time in its history, the North Atlantic Treaty Organization (NATO) invoked Article 5, allowing its members to respond collectively in self-defense, and on October 7 the U.S. and allied military forces launched an attack against Afghanistan (seeAfghanistan War). Within months thousands of militants were killed or captured, and Taliban and al-Qaeda leaders were driven into hiding. In addition, the U.S. government exerted great effort to track down other al-Qaeda agents and sympathizers throughout the world and made combating terrorism the focus of U.S. foreign policy. Meanwhile, security measures within the United States were tightened considerably at such places as airports, government buildings, and sports venues. To help facilitate the domestic response, Congress quickly passed the USA PATRIOT Act (the Uniting and Strengthening America by Providing Appropriate Tools Required to Intercept and Obstruct Terrorism Act of 2001), which significantly but temporarily expanded the search and surveillance powers of the Federal Bureau of Investigation (FBI) and other law-enforcement agencies. Additionally, a cabinet-level Department of Homeland Security was established.

Despite their success in causing widespread destruction and death, the September 11 attacks were a strategic failure for al-Qaeda. Following September 11, al-Qaeda—whose name in Arabic means “the base”—lost the best base it ever had in Afghanistan. Later some in al-Qaeda’s leadership—including those who, like Egyptian Saif al-Adel, had initially opposed the attacks—tried to spin the Western intervention in Afghanistan as a victory for al-Qaeda. Al-Adel, one of the group’s military commanders, explained in an interview four years later that the strikes on New York and Washington were part of a far-reaching and visionary plan to provoke the United States into some ill-advised actions:

Such strikes will force the person to carry out random acts and provoke him to make serious and sometimes fatal mistakes.…The first reaction was the invasion of Afghanistan.

But there is not a shred of evidence that in the weeks before September 11 al-Qaeda’s leaders made any plans for an American invasion of Afghanistan. Instead, they prepared only for possible U.S. cruise missile attacks or air strikes by evacuating their training camps. Also, the overthrow of the Taliban hardly constituted an American “mistake”—the first and only regime in the modern Muslim world that ruled according to al-Qaeda’s rigid precepts was toppled, and with it was lost an entire country that al-Qaeda had once enjoyed as a safe haven. And in the wake of the fall of the Taliban, al-Qaeda was unable to recover anything like the status it once had as a terrorist organization with considerable sway over Afghanistan.

Bin Laden disastrously misjudged the possible U.S. responses to the September 11 attacks, which he believed would take one of two forms: an eventual retreat from the Middle East along the lines of the U.S. pullout from Somalia in 1993 or another ineffectual round of cruise missile attacks similar to those that followed al-Qaeda’s bombings of American embassies in Kenya and Tanzania in 1998. Neither of these two scenarios happened. The U.S. campaign against the Taliban was conducted with pinpoint strikes from American airpower, tens of thousands of Northern Alliance forces (a loose coalition of mujahideen militias that maintained control of a small section of northern Afghanistan), and more than 300 U.S. Special Forces soldiers on the ground working with 110 officers from the Central Intelligence Agency (CIA). In November, just two months after the September 11 attacks, the Taliban fell to the Northern Alliance and the United States. Still, it was just the beginning of what would become the longest war in U.S. history, as the United States tried to prevent the return of the Taliban and their al-Qaeda allies.

In December 2001, faced with the problem of where to house prisoners as the Taliban fell, the administration decided to hold them at Guantánamo Bay, which the U.S. had been leasing from Cuba since 1903. As Secretary of Defense Donald Rumsfeld put it on December 27, 2001, “I would characterize Guantánamo Bay, Cuba, as the least worst place we could have selected.” Guantánamo was attractive to administration officials because they believed it placed the detainees outside the reach of American laws, such as the right to appeal their imprisonment, yet it was only 90 miles (145 km) off the coast of Florida, making it accessible to the various agencies that would need to travel there to extract information from what was believed to be a population of hundreds of dangerous terrorists. Eventually, some 800 prisoners would be held there, although the prison population was reduced to less than 175 by the time of the 10th anniversary of the September 11 attacks.

In his State of the Union speech on January 29, 2002, President Bush laid out a new doctrine of preemptive war, which went well beyond the long-established principle that the United States would go to war to prevent an adversary launching an attack that imminently threatened the country. Bush declared:

I will not wait on events while dangers gather. I will not stand by as peril draws closer and closer. The United States of America will not permit the world’s most dangerous regimes to threaten us with the world’s most destructive weapons.

Bush identified those dangerous regimes as an "axis of evil" that included Iran, Iraq, and North Korea. At the graduation ceremony for West Point cadets on June 1, 2002, Bush elaborated on his preemptive war doctrine, saying to the assembled soon-to-be graduates and their families, “If we wait for threats to fully materialize, we will have waited too long.” Bush believed that there would be a “demonstration effect” in destroying Saddam Hussein’s regime in Iraq that would deter groups like al-Qaeda or indeed anyone else who might be inclined to attack the United States. Undersecretary of Defense Douglas J. Feith later explained,

What we did after 9/11 was look broadly at the international terrorist network from which the next attack on the United States might come. And we did not focus narrowly only on the people who were specifically responsible for 9/11. Our main goal was preventing the next attack.

Thus, though there was no evidence that Saddam Hussein’s government in Iraq had collaborated with al-Qaeda in the September 11 attacks, the United States prepared for conflict against Iraq in its global war against terror, broadly defined.

On March 19, 2003, on the eve of the invasion of Iraq, President Bush issued the order for war:

For the peace of the world and the benefit and freedom of the Iraqi people, I hereby give the order to execute Operation Iraqi Freedom. May God bless the troops.

On March 20 the American-led invasion of Iraq began. Within three weeks U.S. forces controlled Baghdad, and the famous pictures of the massive statue of Saddam Hussein being toppled from its plinth were broadcast around the world.

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On September 11, 2001, members of a terrorist group called al-Qaeda hijacked, or took over, four airplanes in the United States. The terrorists flew two of the planes into the World Trade Center in New York City. The third plane was flown into the Pentagon, near Washington, D.C. The fourth plane crashed in a field in Pennsylvania. The attacks were the deadliest terrorist act up to that time. About 3,000 people were killed.

On September 11, 2001, the United States suffered the deadliest terrorist attacks on its soil in the country’s history. The attacks, perpetrated by 19 militants associated with the Islamic extremist group al-Qaeda, involved a series of airline hijackings and suicide attacks against targets in New York City and Washington, D.C. The attacks caused extensive death and destruction and triggered an enormous U.S. effort to combat terrorism.